Ok I know I need about 10-15x the volume in return flow. So my question is before I buy should I go with the mag 18 or 12? The 18 is about 1100 gph at 5' of head and the 12 is 800. I have a 112g DT and about a 30g sump -/+ rock and sand I'll say between 115-125. Could be wrong lol. I'm at bout 5' of head from bottom of sump up to the return tee adding in the length of the tee. I have a aqua c ev 240 with an 1100 gph pump on it. I'm trying to make up for the draining it does cause it wants to suck my sump dry on the pump side. I don't want the 18 to be overkill but I don't want the 12 to be to week for the skimmer and can't keep up wit the skimmer. So should I just get th 18 and if it turns out to powerful just in stall a valve?